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STREAM TO SEA ACTIVITY High School British Columbia Species: Native, Introduced or Invasive? The Case of Stickleback Pairs in B.C. BACKGROUNDER The stickleback is abundant in coastal waters throughout the northern hemisphere, and has fascinated scientists since it was first formally described by Linnaeus in 1758. Researchers have used the stickleback as a model organism for studying many topics including: mate choice and courtship; learning and cognition; evolution and speciation and, more recently, environmental monitoring, genetics and gene mapping. “These fish have been compared to the Galapagos Finches of Darwinian fame”!1 The Habits of Sticklebacks One unique aspect of sticklebacks is that in several ecosystems they are a pair of species. There is a benthic (bottom-feeding) species and a limnetic (openwater feeding) species. The benthic species forage along the bottoms of the shallow margins of the lake foraging for relatively large prey such as snails, clams and dragonfly nymphs. The benthic species eat similar food types throughout their life, shifting to larger prey as they themselves get bigger. The limnetic species feeds on tiny plankton at the lake edge among the reeds and submerged plants when it is young. Here the young stickleback can hide from predators such as cutthroat trout. As individuals get older the limnetic species hunts in large schools in the open waters of lakes. There they feed on water fleas and other tiny animals. Since they have different diets in the same lake, and feed in different places, the two species of stickleback do not compete with one another. Process of Evolution Stickleback species pairs are among the youngest species on earth.2 In the life sciences, species are said to ‘evolve’ when there is a change in the traits of living organisms over generations. Stickleback pairs evolved at the end of the last glaciation – 13,000 years ago which is relatively quick since species usually takes millions of years to evolve. As the glaciers receded some of the young sticklebacks stayed in lakes and streams surviving without a migration to the sea. These would later be known as the benthic species. When shifting sea levels restored access to the sea a second population ‘invaded’, probably the limnetic species. The benthic population did not see these ‘new’ sticklebacks as potential 1 From Royal British Columbia Museum web-site on Nov. 9, 2006 2 Brochure published by the Habitat Conservation Trust Fund , February, 1999. http://wlapwww.gov.bc.ca/wld/documents/stickleback.pdf 1 mates and two distinct species may have evolved. In British Columbian the life histories of at least four pairs of sticklebacks have been described. There are species pairs living in Enos Lake, Paxton Lake and lakes connected by Vanada Creek [Priest, Balkwill, Emily lakes]. The Hadley Lake species are extinct. Two Ways Stickleback Populations Have Been Altered Catfish, an invasive species, caused the extinction of stickleback species in Hadley Lake, BC. Species pairs in other lakes are also threatened by invasive species such as pumpkinseed fish, sunfish and brown bullheads. Crayfish are a threat in Enos Lake. The second threat is land development causing effects like soil erosion. The species pairs have been responding to the increased turbidity in the lakes in which they live by hybridizing thus reducing two populations to one. One hypothesis is that turbidity may make it impossible for females to differentiate the males of each species and thus interbreeding occurs. Another hypothesis is that since crayfish in Enos Lake have eaten all the vegetation, the two species were forced to breed in the same microhabitats (benthics species normally nest under vegetation) increasing hybridization. Ethical, Responsible and Cooperative Behaviour University of British Columbia professor Paul M. Wood argues that current legislation in Canada is unlikely to conserve unique and rare species like stickleback pairs. “On a case by case basis, the perceived value of individual species can seldom compete with the value of the development projects that annihilate them. Increment by increment, development continues to win and species lose.” (Lovejoy in Wood in Perspective, p 6) Scientists seem to agree that nothing less than a change in paradigms is required. We have to begin seeing humans as part of an intricate and diverse web rather than as resource developers in an endlessly providing world. Humans must value an economy that depends on a healthy environment not one that proceeds independently from it. “ Biodiversity is valuable precisely because it is a necessary, precondition for the long-term maintenance of the biological resources upon which humans depend. It should be given priority and not traded-off against resource values, as if they were on the same logical plane.” (Wood in Perspectives, p. 6) Marveling at the evolution of stickleback pairs, loving the bright red throats and blue eyes of mating males and being fascinated by their feeding behaviours are ways in which we can come to appreciate another creature in the diverse ecosystems in which we live. When these attitudes of wonder spread, humans may conserve species and ultimately their own health. 2